CONTROL OF THE HOP APHIS. 27 



Nicotine sulphate, 1-3,000 and 1-3,500, in combination with 

 whale-oil soap or flour paste has been successfully used in experi- 

 ments, but it would be safer in practice to use the lower dilutions. 

 In case the greater dilutions are used, careful observations should be 

 maintained to be sure that the spray is doing effective work. The 

 nicotine preparations which come in cans have a slight tendency to 

 settle. In case they do settle and are not thoroughly mixed before 

 measuring, the percentage of active insecticide used in one lot of 

 spray may be enough less than should be present in a uniform portion 

 to render the spray ineffective. It is advisable, therefore, to be sure 

 that these preparations are thoroughly mixed before measuring. 



MIXING NICOTINE SOLUTIONS AND WHALE-OIL SOAP. 



During certain spraying experiments with tobacco extracts and 

 whale-oil soap some difficulty was experienced in mixing the concen- 

 trated solutions of blackleaf tobacco and whale-oil soap. When 

 these were combined a greenish-gray precipitate of a flocculent nature 

 was formed. A similar precipitate occurred when one of the mate- 

 rials was diluted and the other left concentrated. When each solu- 

 tion was diluted to half of the final amount, however, this objec- 

 tionable nozzle-clogging precipitate did not appear. 



Flour paste does not have this effect, but when whale-oil soap is 

 used as a spreader for tobacco sprays, both solutions must be well 

 diluted before mixing. 



PREPARATION OF THE FLOUR PASTE. 



In preparing the flour paste, mix a cheap grade of wheat flour 

 with cold water, making a thin batter without lumps, or wash the 

 flour through a wire screen with a stream of cold water. Dilute until 

 there is 1 pound of flour in each gallon of mixture. Cook until a 

 paste is formed, stirring constantly to prevent caking or burning. 

 (See PI. VI, fig. 1.) Add sufficient water to make up for evaporation. 



If the paste is not sufficiently cooked, the resulting spray will not 

 be effective. If overcooked, the paste will harden when thoroughly 

 cool; it will then not mix with water very readily. Usually, how- 

 ever, the paste is used as it is prepared, and overcooking is not a 

 disadvantage. 



When mixed in a spray tank flour paste has a tendency to settle, 

 and in order to do satisfactory work agitation is necessary. This is 

 only a slight disadvantage, however, and is necessary with most spray 

 materials. The large spray tanks are usually fitted with an agitator, 

 and a hoe makes an effective agitator for the 50-gallon barrels, so that 

 this problem is a simple one. 



